doc: update README.md and CONTRIBUTING.md in response to review comments

I didn't 'add' these files before my final mail.

Change-Id: Id6f25629638e58421a3dee7632aec38aad9b1970
Reviewed-on: https://go-review.googlesource.com/1340Reviewed-by: Andrew Gerrand <adg@golang.org>

CONTRIBUTING.md

@@ -24,6 +24,6 @@ before sending patches.
 **We do not accept GitHub pull requests**
 (we use [Gerrit](https://code.google.com/p/gerrit/) instead for code review).
 
-Unless otherwise noted, the Go source files ared istributed under
+Unless otherwise noted, the Go source files are distributed under
 the BSD-style license found in the LICENSE file.
 

README.md

 # The Go Programming Language
 
+Go is an open source programming language that makes it easy to build simple,
+reliable, and efficient software.
+
 ![Gopher image](doc/gopher/fiveyears.jpg)
 
 For documentation about how to install and use Go,
-visit http://golang.org/ or load doc/install-source.html
+visit https://golang.org/ or load doc/install-source.html
 in your web browser.
 
 Our canonical Git repository is located at https://go.googlesource.com/go.
 (There is a mirror of the repository at https://github.com/golang/go.)
 
-Please report issues here: https://github.com/golang/go/issues
+Please report issues here: https://golang.org/issue/new
 
 Go is the work of hundreds of contributors. We appreciate your help!
 
 To contribute, please read the contribution guidelines:
-	http://golang.org/doc/contribute.html
+	https://golang.org/doc/contribute.html
 
 Unless otherwise noted, the Go source files are distributed
 under the BSD-style license found in the LICENSE file.
@@ -25,9 +28,9 @@ under the BSD-style license found in the LICENSE file.
 
 If you have just untarred a binary Go distribution, you need to set
 the environment variable $GOROOT to the full path of the go
-directory (the one containing this README).  You can omit the
+directory (the one containing this file).  You can omit the
 variable if you unpack it into /usr/local/go, or if you rebuild
-from sources by running all.bash (see doc/install.html).
+from sources by running all.bash (see doc/install-source.html).
 You should also add the Go binary directory $GOROOT/bin
 to your shell's path.